The “Evolution” of the Trilobite Strettonia Comleyensis

ISSN 1750-855X (Print) ISSN 1750-8568 (Online)

The “evolution” of the trilobite Strettonia comleyensis

Steve G. Butler1, Keith A. Hotchkiss2 & Adrian W.A. Rushton3

BUTLER, S.G., HOTCHKISS, K.A. & RUSHTON, A.W.A. (2012). The “evolution” of the trilobite Strettonia comleyensis. Proceedings of the Shropshire Geological Society, 17, 22–32. Strettonia comleyensis is a species of trilobite, discovered and described by Edgar Sterling Cobbold from Comley, Shropshire, of which only the head and an associated pygidium were available for description. Other specimens have since been found in Morocco and Poland, but the genus and species remains fairly rare. In 2009 a non-scientific attempt was made to construct the missing thorax in order to use it on commercial products. This article documents the evolution (ontogeny) of this process and the stages, illustrations and comments involved.

1Red Willow, Heighways Lane, All Stretton, Shrophire SY6 6HN. E-mail: [email protected]. 2Windy Ridge, Farm Lane, All Stretton, Shropshire SY6 6HN. E-mail: [email protected]. 3c/o Natural History Museum, London SW7 5BD. E-mail: [email protected].

INTRODUCTION STRETTONIA COMLEYENSIS Edgar Sterling Cobbold D.Sc., A.M.I.C.E., Philip Lake, author of the monograph Cambrian F.G.S., 1851–1936 (Figure 1), was an amateur Trilobites, 1906–46, gives the following local geologist, who, through dedicated and introduction to Strettonia (Figures 3 and 4): distinguished work on the Cambrian of the Comley and Wrekin areas, gained much “The genus Strettonia was established by international recognition. A retired civil Cobbold in 1931 with a new species Strettonia engineer, Cobbold was noted for his work on comleyensis, as the genotype. He thought that the Elan Valley Aqueduct scheme [during this Olenoides (Dorypyge) desiderata Walcott might time he was mentor for Charles Lapworth’s son also belong to it. He remarked that the genus Herbert, the link between geology and civil seems to be “nearest to Centropleura in some engineering thus developing through the details and to Dorypyge in general build.” synergies between these men (de Freitas & Along with the cranidia of Strettonia a tail was Rosenbaum, 2008) Ed.]. also found. At first he thought that this belonged to the same species, but afterwards he was more inclined to refer it to Protolenus. COMLEY QUARRY The real affinities of the genus are very The quarry at Comley (Figure 2), 3 km north- uncertain and I leave any discussion till after east of Church Stretton, is of international the description of the genotype.” significance. Cobbold conducted in total 63 excavations in the area, of which trench No. 2, In the discussion mentioning the associated 200 yards south of Comley Quarry, is the site at pygidium, Lake further states … “At first which he found Strettonia comleyensis in the Cobbold thought that it belonged to that Lower Cambrian Protolenus Limestone. This species, but afterwards he came to the particular trench (Excavation No. 2) has been conclusion on rather insufficient grounds that it reopened at least twice since 1931: once in 1962 was more likely a tail of Protolenus. If Matthew (Matthews, 1963) and again in 2008 (Siveter, (1892) was right in placing Olenus zoppi pers. comm.). However no further specimens of Menhegini in Protolenus it is clear that the species have been reported (Rushton, pers. Cobbold’s first thoughts were best.” comm.). Following this line of reasoning it was decided to use that pygidium (tail) in the construction of the “complete” Strettonia.

THE TRILOBITE STRETTONIA COMLEYENSIS

Figure 1. Photograph of E.S. Cobbold taken by American geologist Dr. C.E. Resser (undated). From the frontispiece of Watts (1936).

S.G. BUTLER, K.A. HOTCHKISS & A.W.A. RUSHTON

Figure 2. Photograph of Comley Quarry on 30th May, 1896, taken on the occasion of the visit by Cambridge University to Mason College (later to become Birmingham University) at the start of the joint research project to establish the evolution of graptolites in relation to Lower Palaeozoic stratigraphy. Cobbold was later to include this site in his mapping of the Caer Caradoc region, published 1927 and still regarded as the most detailed study. This photograph includes Prof. Charles Lapworth, the principal investigator of the research and Prof. Tom McKenny Hughes, Woodwardian Professor of Geology at Cambridge University and his five bright final year students (all female, hence the presence of McKenny Hughes’s wife as chaperone!), who were to work on the project and subsequently publish papers which were to become benchmarks for Lower Palaeozoic stratigraphy for the next five decades.). The photographer was W. Jerome Harrison, curator of Lapworth Museum. Photograph reproduced by kind permission of the Curator of the Lapworth Museum, Birmingham.

______Scale line = 4 mm Scale line = 6 mm

Figure 3. Supposed pygidium of Strettonia, with spines Figure 4. Cranidium, type specimen of Strettonia comleyensis restored from the counterpart. (From Cobbold, 1931, pl. 40). Cobbold, test preserved. (From Lake 1940, pl. 42).

THE TRILOBITE STRETTONIA COMLEYENSIS

ADDING A THORAX TO STRETTONIA plate XLII, figures 12-16. Subsequent workers Adrian Rushton, an internationally renowned have made reconstructions, based on the figures expert on Cambrian trilobites, was approached I have mentioned, but I am not sure how to see if he would give advice in the trustworthy they are. However, they may be the reconstruction of a complete Strettonia. He easiest source from which to make a design or kindly agreed to do this and over the ensuing six emblem, if that is what you need. It is possible months the following correspondence led to the that there is a reconstruction in one of Pierre development of a hypothetical thorax for Hupé’s Memoirs of 1953 (Notes et Mémoirs, Strettonia comleyensis. Service géol Maroc (Rabat), no. 103; or During this period of development, several Annales de Paléontologie, vol. 39). I do not modifications were suggested and rejected, have a copy of those works and cannot check involving the proportions of the thorax to the them. Another resource is to consult the web rest of the body, until a reasonably satisfactory pages by Sam Gon III. He has been making conclusion was reached. The whole exercise has idealised drawings of trilobites and he may have to be judged in the light of its use as a non- tried his hand on Strettonia. scientific artefact. I hope this helps you. And if by chance you The account which follows charts this find a good specimen of Strettonia comleyensis I development through correspondence between hope that you will let me see it and possibly the authors, which includes emails and letters, make a photograph. The genus is in need of some of which were undated. Various ideas revision.” were postulated and rejected or developed over SGB to AWAR (undated): initial drawing sent the period March 2008 to April 2009. to AWAR after receiving the above. This being the first sketch of the unknown thorax (Figure CORRESPONDENCE LEADING TO THE 5). EMBLEM Samples of our correspondence follow: AWAR = Adrian Rushton; KAH =Keith Hotchkiss; SGB = Steve Butler.

Red italic print alongside diagrams are transcripts of AWAR’s handwritten comments.

AWAR to KAH (20 Jun 08): the first communication introducing known ideas about Strettonia.

“Strettonia is fairly rare and the known specimens are fragmentary. I know of: (1) Cobbold’s specimens (in the Sedgwick Museum in Cambridge), of which he recorded about 20 fragments, and elsewhere, (2) one fragment from Morocco, and (3) a record of deformed fragments from Poland. Cobbold’s photos in the Quarterly Jl Geol. Soc. London, 1931, pl. xl, figs 5-10, are better than nothing, but not brilliant (one could do better nowadays). Lake’s Monograph of British Cambrian Trilobites (Palaeontographical Figure 5. Strettonia comleyensis: hypothetical image referred to about 22 Jun 2008. Society, London, 1940) has good wash- drawings that are easier to interpret: see his

S.G. BUTLER, K.A. HOTCHKISS & A.W.A. RUSHTON

AWAR to KAH (24 Jun 08): (referring to Figure 6); in response to the first sketch - this “I have roughly marked my suggestions on a also develops ideas about head and pygidium as copy of the reconstruction” (Figure 6) “and will well. post it to you. Take them or leave them as you like – we know it is a speculative reconstruction. “Thanks for sight of the image. It is fairly well The fact that we know so little about Strettonia imagined, but needs some polishing, as follows: is the reason why I hope to see more material some day.” 1. The cranidium is known to have an anterior border and furrow, but these have not been represented. I would expect these features to continue round the sides of the head-shield

2. I think you should at least represent the anterior facial sutures, even if their course is a mere guess.

3. I also think the eye-lobe is shown as a bit longer and more curved than the sources warrant.

4. The glabella should be widest at its mid- length, namely at the third lobe (L3) from the neck-ring in Lake’s figures, whereas in your image it is widest at L2. Additionally the inter-ocular genae (the area between the glabella and the eye) are shown too wide.

5. The posterior glabellar furrow is longer and more curved than your figure suggests.

6. The thoracic axis might be expected to taper backwards and the pleurae on each segment should show pleural furrows. Figure 6. Strettonia comleyensis: hypothetical image referred to on 24 Jun 2008. 7. The pygidial axis is shown slightly too short compared with Cobbold’s figure and the pleural region is shown as much too wide – such that the pygidial width is shown as nearly twice as wide at its anterior edge as the axis, whereas in Cobbold’s figure the axis is about three-quarters as wide as the pygidium.

8. Finally, the thorax, as it is drawn, does not convincingly match the pygidium. The last thoracic segment needs to wrap neatly round the front of the pygidium. This would look natural if the thorax tapered backwards, as suggested above.”

THE TRILOBITE STRETTONIA COMLEYENSIS

AWAR to KAH (undated, referring to Figure 7): the posted annotations commented on above are elaborated upon.

Figure 7. Strettonia comleyensis: hypothetical image referred to at the end of June, 2008.

AWAR to KAH (11 Jul 2008): (referring to Figure 8); noting errors in the glabella and an unidentified problem with the pygidium.

“Of the latest drawings I like the look of the head in figure a) – the shape of the glabella and the eye–lobes are recognisable and distinctive.”

Figure 8. Strettonia comleyensis: hypothetical image referred to on 11 Jul 2008.

S.G. BUTLER, K.A. HOTCHKISS & A.W.A. RUSHTON

“However I think the glabella is a bit too 3. The most awkward part of the drawing is narrow compared with the width between the back of the glabella (the occipital ring) glabella and eye. In Lake’s fig. 12 the distance and the manner in which the front of the to the farthest- out part of the eye is still less thorax abuts the back of the head. This looks than the width of the glabella. unnatural because the first thoracic segment The thorax looks a bit more convincing in fig. is shown much longer, front-to-back, than the b), the spines on the thoracic spines being subsequent segments. Also the furrow that neater and more compact, and the pygidium crosses the posterior end of the glabella, the (tail piece) fits better onto the thorax. But both “occipital furrow”, usually lies just forward figures show the pygidial axis too narrow of the transverse furrow at the back edge of compared with Cobbold’s and Lake’s figures. At the fixed cheeks; the drawing shows them as the front edge the axis takes up about ¾ of the forming a single straight line. total width, whereas even in your fig.b) it is about ½. I will mark a copy of the latest image and post it Finally, there is something strange about the to you.” appearance of the librigenae (free cheeks): I can’t explain in writing, so will send a letter. This view is of course completely subjective as we have not got the free cheeks (and no proof that the head and tail belong either).”

AWAR to KAH (22 Jul 08): (referring to Figure 9); this is selective text as it was part of correspondence referring to other matters. Here it is suggested for the first time that the thorax be elongated.

“………… the tail piece (pygidium) should be shown as smaller than the head - as you already have it - even though among Cobbold’s specimens the heads and tails are more nearly the same size...... (there might) be a case for adding two or three more segments in the thorax so that the backward taper is more gradual; but as an emblem, I prefer it as it is. Figure 9. Strettonia comleyensis: hypothetical image referred to on 22 Jul 2008.

I do have two or three points to suggest in order to make the Strettonia a bit more “natural”: SGB to AWAR (undated): referring to Figure

10; this in response to a sketch from AWAR and 1. The frontal outline needs to be a flatter being the first attempt which appeared to have curve, with the frontal rim coming closer to better balanced proportions. the front of the glabella.

“I have elongated the thorax by adding 4 extra 2. The two pairs of glabellar furrows nearer segs and at this stage have not taken too much the back should be a little longer, the space care with details (anterior glabellar margin is between their inner ends being 1/3 of the still wrong), but am interested in your comments glabellar width. They could be set a tiny bit on its overall shape & size e.g. ratio pygidium: farther forwards too. head. It may still be shapely enough to grace the

front of some local artefact!”

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AWAR to SGB (undated, in response to Figure 10): the suggestions are reflected in Figure 11, which shows a reduced thorax and larger pygidium, but is rather sketchy.

“...... your new version looks most convincingly trilobite-like. I like the way you have graded the width and length of the thoracic segments...... Nevertheless I suggest that you try providing only 9 or 10 segments in the thorax whilst enlarging the pygidium Figure 10. Strettonia comleyensis: hypothetical image somewhat, perhaps to about 1.5 times or more referred to at the end of July, 2008. of its present width. This would give a more “corynexochid” look to the whole trilobite and would not be out of keeping with the actual ratio in size of the known cranidia and pygidia.”

Figure 11. Strettonia comleyensis: hypothetical image referred to at the beginning of August, 2008.

S.G. BUTLER, K.A. HOTCHKISS & A.W.A. RUSHTON

AWAR to SGB (undated); in response to Figure 11 and amendments made in Figure 12.

“I liked that 10-segment draft even better than the 12-segment one you sent earlier. If I may, I will make two suggestions about it.” – these are shown in Figure 12.

Figure 12. Strettonia comleyensis: hypothetical image referred to in August, 2008.

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AWAR to SGB (3 Oct 08): in response to Figure 12, with amendments shown in Figure 13. This latter being the final attempt; the problem with the pygidium probably refers to the earlier attempt in Figure 11.

Figure 13. Strettonia comleyensis: hypothetical image referred to on 3 October, 2008.

at the NHM, at least for the moment, because I AWAR to SGB (undated): referring to Figure want to use it in the presence of Richard Fortey 13. and see what he makes of it. I expect him to look keenly at it, but remain puzzled, because “I think your latest drawing is admirable. It Strettonia is quite a peculiar trilobite, and not shows what is known and what may fairly be well known.” guessed (making reasonable assumption- notably that the tail is correctly assigned to the head). The reconstruction looks sensible and is convincingly conceived. I see that it now has a shorter, more Dorypyge-like, thorax. I hope it does its job as an emblem and that someone, somewhere, will find an articulated specimen. In the meantime we have yours!”

AWAR to KAH (undated): referring to Figures 14 and 15. Figure 14. Strettonia comleyensis: the design for the mug.

“The mug is a very neat production with a discreetly informative colouring. I will keep it

S.G. BUTLER, K.A. HOTCHKISS & A.W.A. RUSHTON

Shropshire. Palaeontology, 16(1), 139–148, pls. 8–9. Moore, R.C. (ed.) (1959). Treatise on Invertebrate Palaeontology. Part O. Arthropoda 1. Geological Society of America and University of Kansas Press, Boulder, Colorado, and Lawrence, Kansas, xix + 560pp. Watts, W.W. (1936). Edgar Sterling Cobbold. Transactions of the Caradoc and Severn Valley Field Club, 1pl., 13pp.

Figure 15. Strettonia comleyensis: the mug itself.

REFERENCES

Cobbold, E.S. (1927). Stratigraphy and geological structure of the Cambrian area of Comley, Shropshire. Quarterly Journal of the Geological Society, 83(4), 551–573. Cobbold, E.S. (1931). Strettonia comleyensis, Cobbold, Quarterly Journal of the Geological Society, 87, p.473, pl. xl, figs. 5– 10. de Freitas, M.H. & Rosenbaum, M.S. (2008). Engineering Geology at Imperial College London; 1907–2007. Quarterly Journal of Engineering Geology & Hydrogeology, 41(2), 223–228. Fortey, R.A. & Owens, R.M. (1992). The trilobite Angelina Unstretched. Geology Today, Nov.-Dec., 219–221. figs. 1–7. HUPÉ, P. (1953). Contribution à l’ étude du Cambrien inférieur et du Précambrien III de l’Anti-Atlas marocain: Service géol. Maroc (Rabat), Notes et Mém, No. 103, 402 pp., 24 pl., 99 fig. Lake, P. (1940). British Cambrian Trilobites. Part XII, Palaeontog. Soc. London. Pp. 298– 300. pl. XLII, 12-16. Matthew, G.F. (1892). Protolenus: a new genus of Cambrian Trilobites. Bull. Nat. Hist. Soc New Brunswick, 10, pp. 34–7. Matthews, S.C. (1973). Lapworthellids from the Copyright Shropshire Geological Society © 2012. Lower Cambrian Limestone at Comley, ISSN 1750-855x